NASA is planning to extend the life of the Voyager 1 spacecraft until 2025 by shutting off the heating system to save power. Voyager 1 was launched on Sept. 5, 1977, about two weeks after Voyager 2 in what was originally planned to be a five-year mission to study Jupiter and Saturn.

The spectrometer, which collects and returns data, aboard Voyager 1 was built to withstand temperatures as low as minus 35 degrees Celsius (minus 31 degrees Fahrenheit), The heater nearest the spectrometer was actually shut off 17 years ago and other heaters in the spacecraft kept the temperature around minus 56 degrees Celsius (minus 69 degrees Fahrenheit.) Scientists believe the termperature inside Voyager 1 will read minus 79 degrees Celsius (or minus 110 degrees Fahrenheit), since that's as low as the thermometer will indicate.

In this gallery, originally posted in 2007, we'll look at some of the more fascinating discoveries of Voyager 1 and Voyager 2.

Credit: NASA/JPL-Caltech

Less than a year ago and over 9.7 billion miles away from Earth, the Voyagers discovered big bubbles, about 100 million miles across, near the edge of our solar system. Voyager 1 entered this foamy area in 2007.

"The sun's magnetic field extends all the way to the edge of the solar system," explains astronomer Merav Opher. "Because the sun spins, its magnetic field becomes twisted and wrinkled, a bit like a ballerina's skirt. Far, far away from the sun, where the Voyagers are now, the folds of the skirt bunch up."

The area of the bubbles is called the "heliospher" which is the border crossing between our solar system and the rest of the Milky Way. Opher believe that these bubbles may protect our galaxy from cosmic rays and other dangers from black holes and supernova explosions.

NASA descibes the drawing: "Old and new views of the heliosheath. Red and blue spirals are the gracefully curving magnetic field lines of orthodox models. New data from Voyager add a magnetic froth (inset) to the mix."

Credit: NASA

In April 2011, NASA announced that the two Voyager spacecraft would soon be the first human-made objects to leave our solar system. While on their journey, each day the Voyagers send back this message, "Expect the unexpedted."

At this point the power left in Voyager 1 from the radioactive decay of a Plutonium 238 heat source was expected to keep it running until 2020.

Credit: NASA/JPL-Caltech

Probably the Voyager image that stunned scientists the most was that of an active volcano on Jupiter's moon Io. The Pioneer probes had detected volcanoes on Io but none were believe to be alive.

Here's a closer look at an inactive volcano on Io. The moon has about 100 times the volcanic activity as Earth.

Scientists made another major discovery on Io, called the Io torus, a ring of ionized sulfur and oxygen which comes from the moon and adds to Jupiter's magnetic field.

This was the closest view of the old and massive storm that gives Jupiter its trademark red spot. The Great Red Spot has been raging on Jupiter for at least 400 years when humans first observed the giant planet. Three Earths can fit into the storm, which is similar to a hurricane. The Voyagers discovered many hurricane-like storm systems rampaging in Jupiter's atmosphere.

Voyager photographed a ring around Jupiter.

The lines that cross Jupiter's moon Europa were first seen by earlier space probes, but Voyager 2 showed that Europa's features were so flat, they "might have been painted on with a felt marker," according to a scientist. It is believed that the planet's surface may be covered by a water ice crust of up to three miles--hiding oceans as deep as 30 miles.

Next stop, Saturn. The Voyagers added to our knowledge of Saturn's moons and signature rings.

This Voyager 1 photo from 1980 showed the fuzzy layer of atmosphere on Saturn's moon, Titan. The Titan findings of the Voyagers helped draw enough interest to send the Cassini spacecraft to Saturn and land a probe on Titan. Cassini is still orbiting Saturn and returning images.

The Voyagers discovered new information about the rings that revolve around Saturn, in particular the twisted F-Ring. One discovery was how the nearby moons affect the structure of the rings.

In January 1986, the first human-made visitor to Uranus was Voyager 2. Left is a true-color view of the planet and a false color view is right.

Some of the most interesting Voyager discoveries were from the many moons orbiting the giant gas planets. One of them is Miranda, the innermost of Uranus' large moons, is about 22,000 miles away from Voyager 2 in this photograph.

This clear-filter, narrow-angle image shows an area about 150 miles across. Two distinct terrain types are visible: a rugged, mountainous region (right) and a lower, striated terrain (left). Craters on the higher terrain show that it is older than the lower terrain. The crater in the lower part of this image is about 15 miles across.

Voyager returned these images of Neptune's rings.

This view of the rings around Uranus shows fine particles throughout the system.

Voyager 2 was Earth's first visitor to Neptune and its Great Dark Spot.

Triton is the largest moon orbiting Neptune. According to readings from Voyager, the moon most likely did not originate from Neptune but was a lost mass that was captured by the huge planet's gravitational force. It's moving in a retrograde orbit which means it spins in the opposite direction of the planet's rotation.

Triton is about three-fourths the size of the Earth's moon. It also has about the same size, density, temperature and chemical composition as Pluto.

The most interesting discovery on Triton's surface was the presence of geyser-like volcanic vents (the black spots) that were apparently spewing nitrogen gas along with fine, dark particles. The Triton dust rose up to five miles high before descending back to the moon's surface. Triton also has a very thin atmosphere.

Voyager 2 revealed storms raging in Neptune's atmosphere. The largest one was named the "Great Dark Spot" which is a storm that's similar to Jupiter's Great Red Spot--including its geographic location on the planet. It has winds up to 1,000 miles an hour.

Astronomers could not locate this storm with the Hubble telescope after it was re-calibrated in 1994.

Voyagers continue to send back data, even after 30 years. The Cosmic Ray Subsystem team studies measurements of cosmic rays left. The data is sensitive to low-energy phenomena in interplanetary space including solar flares. This report is updated Monday-Friday before noon.

Here's a page with links to the most data (top left) returned by the two Voyagers.

Perhaps the greatest adventure of the Voyager program is yet to come. Voyager 1 is 9.7 billion miles from Earth, farther than any human-made object has ever traveled. In 2004, it crossed the heliosphere where solar winds slow as they hit the thin gas that fills the void between the stars. What's next for Voyager? Stargazers who were able to last through the entire movie, Star Trek: The Motion Picture, may already know.

Spoiler: In the movie, Voyager flew into a black hole and was discovered by mechanical life forms who gave it their artificial intelligence and a cloud-like ship. It was called V'ger after the "oy" on its name plate was obscured. V'ger threatened to remove humans from Earth but Kirk and Spock outwit it and save the planet.

In the event that the Voyagers would make the first encounter with an extraterrestrial being, NASA decided to send a "Golden Record" or explanation of where Voyager came from and what our planet is like. Here's what the symbols on the front are supposed to represent.

The contents of the Golden Record were organized by Carl Sagan, the most-recognized astronomer of the 1970s. Here's Earth which is labeled by the contents of our atmosphere.

Some scenes of Earth cities are already dated--even before aliens find them. The Golden Record contained photos, audio and video of nature, everyday life and our achievements to give an idea of what our planet was like in 1977.